An acoustic touchscreen has a touch-sensitive area on which the occurrence and location of a touch on a surface is sensed by the effect of the touch on the transmission of acoustic waves propagated across the surface. FIG. 1 illustrates the operation of a conventional acoustic touchscreen 1, having an active, or “touch-sensitive” area 2. A first transmitting transducer 3a is positioned outside of the touch-sensitive area 2 and acoustically coupled to the surface of touchscreen 1. The transducer 3a sends an acoustic signal in the form of an acoustic wave (or beam) 11a traveling parallel to the top edge, and generally in the plane of, touchscreen 1. Aligned in the transmission path of acoustic wave 11a is a first linear array 13 of acoustically reflective elements 4, each of which partially reflects (by approximately 90 degrees) and partially transmits (i.e., passes through) the acoustic wave 11a, creating a plurality of acoustic waves (exemplary ones shown as 5a, 5b, and 5c) traveling vertically (parallel to the Y-axis) across touch-sensitive area 2.
For simplicity, as used in this specification and claims that follow, an “acoustically reflective” element includes any element which at least partially reflects acoustic wave energy, even if such element may actually pass through nearly all of the wave energy. For example, depending on the size of the touch-sensitive area, the number of elements used in the reflective array, the energy of the acoustic signal and/or other factors, it may be possible that an individual reflective array element reflects as little as 1% or less of an acoustic wave into the touch-sensitive area, while passing through the remaining wave energy to the next successive array element.
Returning to FIG. 1, the spacing of the reflective array elements 4 is variable to compensate for the attenuation of the acoustic waves with increasing distance from first transmitter 3a. Alternately, such compensation may be provided by densely spaced reflective array elements with variable reflective strengths. Upon reaching the lower edge of touchscreen 1, the acoustic waves 5a, 5b, and 5c are again reflected by approximately 90 degrees (shown by arrow 11b) by a second linear array 13 of acoustically reflective elements 4 towards a first receiving transducer 6a, where they are detected and converted to electrical signals for data processing. Along the left and right edges of touchscreen 1 are located a similar arrangement. A second transmitting transducer 3b generates an acoustic wave 12a along the left edge, and a third linear array 13 of acoustically reflective elements 4 creates therefrom a plurality of acoustic waves (exemplary 7a, 7b, and 7c) traveling horizontally (parallel to the X-axis) across touch-sensitive area 2. Acoustic waves 7a, 7b, and 7c are redirected (arrow 12b) by a fourth linear array 13 of acoustically reflective elements 4 towards receiving transducer 6b, where they are detected and converted to electrical signals.
If the touch-sensitive area 2 is touched at position 8 by an object such as a finger or a stylus, some of the energy of the acoustic waves 5b and 7a is absorbed by the touching object. The resulting attenuation is detected by receiving transducers 6a and 6b as a perturbation in the acoustic signal. A time delay analysis of the data with the aid of a microprocessor (not shown) allows determination of the coordinates of position 8. Those skilled in the art will appreciate that it is not essential to have two sets of transmitting/receiving transducers to make a touchscreen. The device of FIG. 1, without one set of transducers, will still function as a touchscreen, detecting the occurrence of a touch and providing limited location information (i.e., one of the coordinates). Or, a touchscreen can be designed with only two transducers by using a common transmit/receive transducer scheme as shown in FIG. 11 of U.S. Pat. No. 4,880,665.
A bezel (outline indicated by a dotted lines 9 and 10 in FIG. 1), typically made of molded polymer or sheet metal, overlays the touchscreen 1, concealing the transmitting and receiving transducers, the reflective elements, and other components, and defining the touch-sensitive area 2. This arrangement protects the concealed components from contamination and/or damage, presents a more aesthetically pleasing appearance, and defines the touch-sensitive area for the user. The touch-sensitive area 2 is surrounded by border regions 15 (only two labeled), where the reflective elements 4 and the transmitting and receiving transducers 3a, 3b, 6a, and 6b are located. Reducing the width of border regions 15 increases the percentage of the frontal area of the device that may be allocated to touch-sensitive area 2, as well as conveying a less cumbersome, sleeker design.
U.S. Pat. No. 6,636,201, which is incorporated herein by reference for all that it teaches, discloses acoustic touchscreens having relatively narrower border regions 15. The key to reducing their width lies with reducing the width of arrays 13 and the transducers (3a, 3b, 6a, 6b). FIG. 2 illustrates a transducer 16 and a reflective array 13 of an acoustic touchscreen that allows for a narrower border region than in conventional touchscreens. In particular, the path of the acoustic wave 11a is confined by an acoustic waveguide core 18. The reflective array 13 includes a plurality of acoustically reflective elements 14 cooperating with the waveguide core 18. In the illustrated embodiment, the reflective elements 14 are overlaid on top of the waveguide core 18 at predetermined intervals, which effectively allows the reflective elements 14 to partially deflect energy from the incoming acoustic wave 11a across the touch-sensitive area as the acoustic waves 5a and 5b. As illustrated in FIG. 3, a significant portion of the acoustic energy is confined to the array 14 of width w as a result of the inclusion of the waveguide core 18 of width y. Because the width of the acoustic wave energy can be controlled by the width of the waveguide core 18, the reflectors 14 may be made correspondingly narrower than conventional ones, but yet deflect a sufficient amount of acoustic energy across the touch-sensitive area for touch-sensing purposes